The in Vitro Effect of Different Implant Heights and Different Buccal-lingual Angulations on the Retentive Properties of an Attachment System in Two-implant Supported Mandibular Overdentures.

Abstract: ABSTRACT Purpose. The aim of this in vitro study was to evaluate the retentive properties of an overdenture attachment system when two implants were placed at different heights (0mm and 3mm) and/or different angulations (0 °and 20°) Materials and Methods. Forty sets of two implants-supported overdenture models were evaluated (N=10 for each group). An acrylic resin block was used to house... read more the overdenture attachments (Locator ®), while an artificial bone block was used to house the two 4.3 × 13mm internally hexed implants (Nobel Biocare). The groups consisted of the following: For Group A :(control group), implants were placed parallel to each other and at the same horizontal level; For Group B: implants were placed parallel to each other and at different heights (3mm different); For Group C: implants were placed at different angulations (20°divergence) and at same height; For Group D: implants were placed at different angulations (20°divergence) and at different heights (3mm). The height was pre-determined by the artificial bone block and different abutment collar heights were used to compensate for the difference. The angulations were determined by a digital goniometer in relation to the vertical axis. All angled implants were lingually tilted. Forty pairs of Locator ®) attachments were used and for all groups the pink nylon male was used for standardization purposes. Dislodging cycles were applied to the overdenture attachments system using a texture analyzer that was programmed to apply dislodgment forces to Locator ®) attachment system in a wet condition and to stop cycling when dislodgment force drop below 20 N. The cycles required for the retentive forces of the locator ®) attachments to drop below 20 N were recorded. Two-way ANOVA and four Independent-samples t-tests (α=0.05) between each groups were used to analyze the difference in retentions loss among the four groups. Results. Initial retentive forces for all groups ranged from 60N to 68N. For the main effect of height and angulations, the results of Two-way ANOVA were significant and there was an interaction between different heights and angulations of implants. The results of the Independent samples t-tests revealed significant differences for the number of cycles required for initial retentive forces to drop below 20 N between groups (C and D), (A and C), and (B and D), while there was no significant difference between groups (A and B). Conclusions. The results of this in vitro study demonstrated that the different heights and angulations negatively affect attachment retention capacity. Groups A and B showed the greatest longevity, while group D showed the shortest longevity. read less

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